258 FIRST YEAR COURSE IN GENERAL SCIENCE 



leaves of plants. There are other waste products which are 

 disposed of in different ways. The removal of waste pro- 

 ducts which would hinder oxidation is a part of nutrition; the 

 process is called excretion. 



282. Residue Left from Food. When coal is the fuel 

 used in a furnace, besides the waste product in the form of 

 gas, there is a residue which can not be oxidized to give 

 heat. This residue of clinkers, stones, and ashes cannot be 

 burned, and is of no use as fuel. The bodies of living things 

 take in, with their food, substances which never become a part 

 of the body and are never oxidized. This residue is expelled 

 from animal bodies from the lower end of the intestine; 

 in plants it collects in the leaves and is removed when the 

 leaves fall. 



283. Protoplasm. No matter how different from one an- 

 other the many forms of plant and animal life may be, they 

 are all alike in one particular: they are largely composed of 

 a kind of matter called protoplasm. Protoplasm is not life 

 itself, but it is the only material in which life is known to 

 occur. Protoplasm is a colorless liquid, nearly transparent, 

 about as thick as the white of a raw egg. There are minute 

 living bodies which consist of nothing but protoplasm. Most 

 living things, however, consist of protoplasm and certain 

 other substances made by it, such as sugar, fat, the wood of 

 a plant, or the shell of an oyster. 



284. The Composition and Behavior of Protoplasm. 

 Chemists have studied the composition of protoplasm and 

 have found it to be very complex. It is made up of a num- 

 ber of compounds, which contain some of the commonest 

 elements occurring in the air, in water, and in the earth's 

 crust. These are carbon, hydrogen, oxygen, nitrogen, sul- 

 phur, and phosphorus. 



All protoplasm, whether in plants or animals, has the same 

 appearance, the same chemical composition, and the same 

 physiological properties. But there must also be certain 



